Port status change & Port STP change

[Mavericks]

Hi all,

I have an issue of ports flapping. Timing, switch and port seem to be random. 

The incident on the 18th was a port an AP was on. The incident on the 16th was a different switch and a wired power monitoring device (https://energycurb.com/). In the past it might be some other random wired device. 

In the logs you always see 'Port status change' first then 'Port STP change' with the same time stamp. Does this mean STP is shutting the port or something else is happening?

After speaking with Meraki support it was relayed to me that something wired is causing a loop. They mentioned it would not be possible to determine what device was doing it unless we were able to do a packet capture at the time it was happening. 

Here is my topology, I have two wireless mesh connections (labeled since the lines are hard to see) and I've labeled the root bridge (set manually).

Any ideas for further troubleshooting.

Many many thanks.

[Bruce]

Don't worry too much about the STP messages, that's what you should be seeing. When a port goes down you will see a STP notification that transitions the port from Designated to Disabled. Then when the port comes back up (for an access port) you will see the STP for the port go from Disabled to Designated. 

You are actually seeing the port go down first, then STP make the change. The question needing an answer is why is the port is going down in the first place. What device is it connected to? Is the device a printer or something going into standby, then waking up straight away?

[Mavericks]

Hi @Bruce ,

Thanks for the clarity on the STP log.

For this particular switch (Playhouse) port 2 is a trunk port with an AP connected. I’ve also seen this for the home power monitoring devices I mentioned previously on access ports. I’m less concerned about those as you mention they might go to sleep but the AP flapping caused some issues. 

[Bruce]

I’d check all your cabling. Make sure everything is full pushed home. Swap cables around, see if the issue moves. Test any cable runs you’ve got in walls if you can (use the cable test function in the Meraki switch if you’ve nothing else). Maybe there is a physical issue. Other than that make sure that all the firmware is up to date just in case.

[Mavericks]

The cabling was done a long time ago, I will re-seat everything and run some tests.

So based on the information, you think this is a physical connection issue? And like you mentioned before, since the log is showing the port going down first before the STP message there is no concern of something causing a loop right?

Thanks again for your help. 

[Bruce]

Definitely don’t believe there is a loop, the STP transitions align too well with the change in the physical port status. I’d be checking the cabling for sure, that would be my starting point especially if it’s old. Then once I was satisfied that isn’t the problem I’d look elsewhere.